1. Field of the Invention
The present invention relates to an active matrix type display device. More particularly, the present invention relates to a display device performing gradation display by both voltage gradation and time gradation.
2. Description of the Related Art
Recently, techniques of manufacturing a semiconductor device such as a thin film transistor (TFT) in which semiconductor thin films are formed on an inexpensive glass substrate, have been rapidly progressing. The reason for this resides in that the demand for active matrix type liquid crystal display devices has risen.
An active matrix type liquid crystal display device is a device in which TFTs are placed in each pixel of a pixel region having from several hundreds of thousands to several millions of pixels arranged in a matrix shape, and in which an electric charges input and output to pixel electrodes connected to each pixel TFT are controlled by the pixel TFT switching function.
In recent years, active matrix type liquid crystal display devices have spread from being used as only displays of notebook type personal computers, often seen conventionally, to being used as the display of desktop type personal computers.
There is a demand for the display of a large amount of information (including character information and image information) at once, and the image capabilities of personal computers are being made higher definition and with more gradation levels (preferably full colorization).
Accompanying the increase in personal computer display capabilities, improvements in active matrix type liquid crystal display devices as personal computer display devices are advancing. Digital driver type active matrix liquid crystal display devices with which the interface to a personal computer is easy, and with which high speed driving of the driver is possible, have recently been in the spotlight.
A digital video data is inputted into a digital driver type active matrix liquid crystal display device from a data source such as a personal computer. A D/A converter circuit (DAC: Digital-Analog Converter) for converting an externally inputted digital video data into analog data (gradation voltages) is necessary in an active matrix type liquid crystal display device having a digital driver. Various types of D/A converter circuits exist.
The multiple gradation display capability of an active matrix type liquid crystal display device having a digital driver depends on the capability of the D/A converter circuit. Namely, it depends on how many bits of digital video data is converted into analog data by the D/A converter circuit. For example, in general, display of 22=4 gradations can be performed with an active matrix type liquid crystal display device having a D/A converter circuit which processes 2-bit digital video data, and if the D/A converter circuit processes 8-bit data, then 28=256 gradation display can be performed. Furthermore, it is possible to perform 2n gradation display for n-bit data.
Thus a multiple gradation display of the active matrix type liquid crystal display device, preferably a full color display, has been in demand recently. In order to raise the gradation display capability of the active matrix type liquid crystal display device with a digital driver, it is necessary to raise the signal processing capability of the D/A circuit. However, in order to increase the capability of the D/A converter circuit, the circuit structure of the D/A converter circuit becomes complex, and the layout surface area becomes large.
Liquid crystal display devices in which the D/A converter circuit and the pixel region are formed by polysilicon TFTs on the same substrate have been reported recently. However, if the circuit structure of the D/A converter circuit becomes complex in this case, then the D/A converter circuit yield drops, and so does the yield of the liquid crystal display device. Further, if the surface area for the D/A converter circuit becomes larger, then it becomes difficult to realize a small-scale liquid crystal display device.
The realization of a small-scale active matrix type liquid crystal display device which can accomplish high definition and multiple gradations is desired.
In view of the above stated problems, an object of the present invention is to provide a display device having a digital driver that can realize higher resolution and more gradations.
One of the features of the present invention is that a display device comprising: a pixel region having a plural number of pixel TFTs arranged in a matrix shape; a source driver and a gate driver for driving the plural number of TFTs; and a circuit for converting externally inputted m-bit digital video data into 2mxe2x88x92n pieces of n-bit digital video data (where m and n are both positive integers greater than or equal to 2, and m greater than n), and for supplying the n-bit digital video data to the source driver; wherein: the 2mxe2x88x92n pieces of n-bit digital data is outputted randomly; and a one-frame image is formed by displaying 2mxe2x88x92n subframes formed by the n-bit digital data.
Another one of the features of the present invention is that a display device comprising: a pixel region having a plural number of pixel TFTs arranged in a matrix shape; a source driver and a gate driver for driving the plural number of TFTs; and a circuit for converting externally inputted m-bit digital video data into 2mxe2x88x92n pieces of n-bit digital video data (where m and n are both positive integers greater than or equal to 2, and m greater than n), and for supplying the n-bit digital video data to the source driver; wherein: the 2mxe2x88x92n pieces of n-bit digital data is outputted randomly; a one-frame image is formed by displaying 2mxe2x88x92n subframes formed by the n-bit digital data; and (2mxe2x88x92(2mxe2x88x92nxe2x88x921)) levels of display gradation can be obtained.
Another feature of the present invention is that a display device comprising: a pixel region having a plural number of pixel TFTs arranged in a matrix shape; a source driver and a gate driver for driving the plural number of TFTs; and a circuit for converting externally inputted m-bit digital video data into 2mxe2x88x92n pieces of n-bit digital video data (where m and n are both positive integers greater than or equal to 2, and m greater than n), and for supplying the n-bit digital video data to the source driver; wherein: the 2mxe2x88x92n pieces of n-bit digital data is outputted by a pattern selected randomly from a plural number of output patterns; and a one-frame image is formed by displaying 2mxe2x88x92n subframes formed by the n-bit digital data.
Another feature of the present invention is that a display device comprising: a pixel region having a plural number of pixel TFTs, arranged in a matrix shape; a source driver and a gate driver for driving the plural number of TFTs; and a circuit for converting externally inputted m-bit digital video data into 2mxe2x88x92n pieces of n-bit digital video data (where m and n are both positive integers greater than or equal to 2, and m greater than n), and for supplying the n-bit digital video data to the source driver; wherein: the 2mxe2x88x92n pieces of n-bit digital data is outputted by a pattern selected randomly from a plural number of output patterns; a one-frame image is formed by displaying 2mxe2x88x92n subframes formed by the n-bit digital data; and (2mxe2x88x92(2mxe2x88x92nxe2x88x921) levels of display gradation can be obtained.
In the above-mentioned display devices, a liquid crystal may be used as a display medium. Also, in the above-mentioned display devices, an EL may be used as a display medium.
Also, the above-mentioned display devices can be used in a rear projector having three display devices, a front projector having three display devices, a single stage rear projector having one display device, a goggle type display having two display device, a portable information terminal having a display device, a notebook type personal computer having a display device, or the like.